Is it just the sun?

Is it possible, as some have hopefully proposed, that changes in the sun account for global heating?
    There has been no overall increase in the energy put out by the sun. It is not a variable star (will not become so until it moves toward its red giant stage in about 5 billion years). It is, over human time-scales, remarkably constant, as shown by 31 years of measurement.
    But could sunspots provide a cause of heating, in some more complex way? A Danish space scientist, Eigil Friis-Christensen, published in 1991 a graph showing a close correlation between global temperature and variations in the length of the roughly 11-year sunspot cycle. He and Henrik Svensmark proposed a complex mechanism, involving cosmic rays and cloud cover, by which the sunspot cycle could have this effect. This "natural cause" is much used, usually without understanding its complexity, by deniers of human-caused heating. Others showed that the data were flawed in several ways, and it is now "undisputed" among scientists in this field, including Friis-Christensen, that sunspot-cycle-length and global temperature have actually diverged — gone in different directions on the graph.

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